Patients with cerebrovascular insufficiency (transient ischemic attacks) related to atherosclerosis, oral progestational agents, fluctuations in blood pressure, and intermittent cardiac dysrhythmias, will be studied to determine, if possible, the degree to which these possible precipitants actually trigger episodes of cerebrovascular insufficiency. Patients will be studied by a variety of clinical investigation, including radiographic procedures, radioisotopic, and pharmacological studies, as well as prolonged monitoring of electrocardiogram and systolic blood pressure. Long term follow-up of patients with TIA's are being conducted in order to determine the natural history of this disorder.